The present invention relates to a sheet electrical heating element and more particularly to the structure of woven electrodes of the sheet electrical heating element which are formed by electrically conductive yarns interlaced in the sheet electrical heating element.
In a conventional sheet electrical heating element, there is an electrode of a construction that electrically conductive wires provided at specific intervals among warp yarns in the part of the electrode of the fabric woven through a combination weave face each other in the direction of thickness of the fabric and that further electrically conductive wires provided in parallel with weft yarns are interlaced with said wires so as to combine each of them in the direction of thickness of the fabric, as disclosed in the Japanese Patent Publication No. 16954/1981.
This type of structure of woven electrodes has been considered as effective in increasing the capacity of the electrode.
However, according to this type of structure of woven electrodes, the electrode portion is thick due to the combination weave and, therefore, the sheet electrical heating element with this electrode lacks flexibility and is doubled or folded with difficulty.
Moreover, since the textile weave of the electrode of said prior art heating element is a plain weave which makes the fabric very close and firm, the heating element has the disadvantage that it lacks flexibility, and therefore, feels hard.
In addition to the lack of flexibility, the conventional electrodes easily break because the electrically conductive wires used for the electrode are made of yarns with a single layer of copper foil or tinned twisted gold wire. Accordingly, the heating element provided with this kind of electrode has a weak folding endurance as a whole, and is not suitable for carpets and similar floor coverings which are often folded and moved from place to place.